Process for laying flexible tubular conduits using a plurality of ships

ABSTRACT

A process for laying flexible conduits on an ocean floor by continuous unrolling of the conduit at a laying site from at least one supply ship to a laying ship, wherein the flexible conduit is gradually transferred from the supply ship to a storage means located on the laying ship.

The invention relates to a process for laying flexible conduits, inparticular flexible tubular conduits and cables using in particular alaying ship and at least one supply ship.

This invention applies both to flexible tubular conduits and to cables,in particular to the electric cables, called flexible conduits below.

To assure the transport of fluids, such as, for example, hydrocarbons inoffshore installations, it is known to place flexible tubular conduitson the ocean floor. The laying of flexible tubular conduits is assuredby a laying ship. During the laying, the flexible tubular conduit isstored in a cage assuring its unrolling during the laying. The capacityof such a cage is limited. Once the length of flexible tubular conduitscontained in the cage is unrolled, the laying operations are stoppedmomentarily. It is necessary to note that the interruptions areparticularly detrimental in the case of laying flexible tubularconduits. Actually, one of the many advantages of these flexible tubularconduits resides in the speed of their laying. This speed makespossible, in particular, a short stopping of the laying ship whose dailycost is very high.

On the other hand, it is known to use supply ships to assure the supply,apart from the laying operations of the laying ship. For this purpose,supply (supply or supply vessel in English terminology) ships are usedwhose daily operating cost is very clearly lower than that of the layingship.

The process for laying flexible tubular conduits according to thisinvention is made faster by using ships for supplying the laying shipwith hose at the very site of the laying. Thus, there is full benefitfrom the fact that the laying operation itself of a flexible tubularconduit is very fast. Moreover, it is possible to use several supplyships taking over from each other to supply the laying ship continuouslywith flexible tubular conduits.

The laying ship and/or the supply ship are equipped with means forstoring flexible conduits. For example, at least one cage with avertical axis and/or at least one coil, advantageously motorized andadvantageously with a horizontal axis, are used.

In a first variant embodiment of the process according to thisinvention, the stages of laying and the stages of transferring flexibleconduits are alternated. The loading is performed, for example, on acage for storing flexible conduits on a laying ship. Once the cage isloaded, the laying of the flexible conduit section which is in the cageis performed. When the cage is empty, a new cycle is begun, byrestocking the cage with flexible conduits. It is possible to use aplurality of supply ships shuttling between the port and the laying shipto assure the continuity of the laying operations.

In a second variant of the process according to this invention, thelaying ship directly performs the laying of a flexible conduit which isprovided to it by a supply ship. Advantageously, a new full supply shiptakes the place of the preceding supply ship when the latter is empty.During this time, the empty supply ship is freed or will be restocked inthe port or by another ship.

In a third variant embodiment of the process according to thisinvention, the supply ship or ships simultaneously provide a plurality,for example two, of flexible conduits to the laying ship. A firstflexible conduit is directly laid by a laying ship from the supply ship.The second flexible conduit is stored in a storage means of the layingship, for example, a storage cage with a vertical axis of rotation. Whenthe supply ship does not have any more flexible conduits, the layingship continues the laying from the storage means. During this time, thesupply ship can be resupplied with flexible conduits, for example, in aport, or can be replaced by another supply ship.

In a fourth variant of the process according to this invention, a layingship comprising at least two means of storing flexible conduits, forexample, two cages, is used. Each cage alternately plays the role ofreceiving flexible conduits from a supply ship or from cages for layingflexible conduits on the ocean floor. When the cage assuring the layingof the flexible conduit is empty, the roles of the two cages arereversed.

The use of a first cage for the transfer of the flexible conduit fromthe supply ship to the laying ship and a second cage for laying theflexible conduit makes it possible to assure the optimal continuity ofthe laying process. The reversal of the roles of the cages is arelatively quick process.

Advantageously, cages having a large capacity are used for the processaccording to this invention. In any case, the flexible conduit isunrolled from the supply ship to the laying ship. That is, the flexibleconduit is transferred in a continuous way between the supply ship andthe laying ship, advantageously with an approximately constant linearspeed.

In a first embodiment, the transferred flexible conduit has a shape of asmall chain between the two floating supports. In a second embodiment,the tubular conduit floats between the two floating supports during itstransfer.

The invention mainly has as its object a process for laying flexibleconduits in particular on the ocean floor, characterized by the factthat it comprises the stage of transfer, to the laying site, of aflexible conduit to be laid between at least one supply ship and thelaying ship.

The invention also has as its object a process for laying flexibleconduits, in particular on the ocean floor, characterized by the factthat it comprises a series of stages consisting in:

loading, with a flexible conduit to be laid, a storage means of a layingship from a supply ship;

laying the flexible tubular conduit from the storage means of the layingship.

The invention will be understood better by the description below andaccompanying figures given as nonlimiting examples, of which:

FIGS. 1a and 1b is a diagram illustrating a first variant of the processaccording to this invention;

FIG. 2 is a diagram illustrating a second variant of the processaccording to this invention;

FIG. 3 is a diagram illustrating a third variant of the processaccording to this invention;

FIG. 4a and 4b is a diagram illustrating a fourth variant of the processaccording to this invention.

In FIGS. 1 to 4, the same references have been used to designate thesame elements.

In FIGS. 1 to 4, a process for laying flexible tubular conduits usingtensioning means placed on the vertical part of the path of the flexibletubular conduit has been illustrated. Of course, the use of a standardlaying process does not go outside the scope of this invention.

In the first variant, the process according to this invention comprisesa series of laying stages illustrated in FIG. 1a and of stages oftransferring flexible tubular conduits between a supply ship 19 andlaying ship 1, illustrated in FIG. 1b. A transferring stage of FIG. 1bfollows the laying stage of FIG. 1a, the transferring stage itselffollowed by a laying stage of FIG. 1a, and so on until achieving thelaying of a desired length of flexible tubular conduit 3, or until amomentary interruption of the laying.

In FIG. 1a, an example of laying ship 1 of improved type, comprising inparticular dynamic positioning means 10, has been illustrated.

Ship 1 comprises storage means 2 of flexible tubular conduit 3, guidemeans 4 of flexible tubular conduit 3 and tensioning means 6.

Storage means 2 advantageously comprise a cage of approximatelycylindrical shape with a vertical axis.

The guide means comprise, for example, a wheel, or, as illustrated inthe figure, a chute 4 making it possible for flexible tubular conduit 3to take a vertical path. Between cage 2 and guide means 4, flexibletubular conduit 3 takes the shape of a small chain.

Tensioning means 6 have been placed at the output of guide means 4. Inthe example illustrated in the figure, two tensioning means 6, mountedon a derrick 5 of approximately parallelepipedic rectangular shape, havebeen placed in series. Other shapes, for example, the pyramidal shape,do not go outside the scope of this invention. Tensioning means 6 areplaced vertically downstream from guide means 4, storage means 2 andupstream from a work table 7 making possible the handling of flexibletubular conduit 3. Tensioning means 6 are intended to support the weightof flexible tubular conduit 3 placed vertically up to ocean floor 9.Tensioning means 6 comprise, for example, a plurality of tracks 11. Forexample, each tensioning means 6 comprises 2, 3 or 4 tracks 11 whichexert a tightening force on tubular conduit 3. The simultaneous advanceof tracks 11 exerting the tightening force on tubular conduit 3 makespossible the lowering of tubular conduit 3 along arrow 14.Simultaneously, ship 1 advances, for example, along arrow 15, ship 1being able to move, thanks to dynamic positioning means 10, in anydirection.

The fact of using tensioning means 6 placed vertically makes it possibleto make tubular conduit 3 pass through an opening 8 in ship 1 called themoon pool in English terminology. This arrangement avoids havingtensioning means 6 and chute 4 placed at the back of the ship. A backposition of chute 4 jeopardizes the balance of ship 1.

Ship 1 comprises means making possible the transfer at sea of flexibletubular conduits 3 from a supply ship 19 of FIG. 1b. In the exampleillustrated in FIG. 1a, the transferring means placed in the backcomprise a chute 17, a tensioning means 16. Tensioning means 16comprise, for example, two diametrically opposite tracks.

When ship 1 has used up the amount of stored flexible tubular conduits3, internal storage means 2, the laying of conduits 3 symbolized byarrow 14 and the advance of ship 1 symbolized by arrow 15 are stoppedsimultaneously. The stopping of the laying is performed while keepingthe end of the flexible tubular conduit on ship 1. The initialization ofthe transfer is obtained by bringing one end of flexible tubular conduit3 from supply ship 19 to laying ship 1. For example, a cable attached tosaid end which is going to be attached to a cable pulled by a winch, istransferred. By pulling on the cable, the end of flexible tubularconduit 3 is brought aboard laying ship 1. Conduit 3 passes bytensioning means 16 to go toward storage cage 2. The transferillustrated in FIG. 1b uses storage means (not represented in thefigure) and guide means 4' of supply ship 19 making it possible fortransferred flexible tubular conduit 3 to form a small chain ending inthe transfer means of ship 1, chute 17 in the example illustrated inFIG. 1. The small chain formed by tubular conduit 3 can be immersed inthe sea water as well as be only suspended in air.

Advantageously, during the transfer, the complete loading of the cage ofship 1 is performed. Thus, the number of end fittings necessary for thelaying of the flexible tubular conduit is reduced.

Supply ship 19 comprises storage means comprising, for example, the sametype as cage 2 or reels. Once the transfer operation is ended, theflexible tubular conduit is brought from cage 2, by guide means 4, andtensioning means 6 at the level of work table 7. At this level, theassembly of the front ends of flexible tubular conduit 3 transferredwith the back end of tubular conduit 3 already laid is performed. Theassembly is performed, for example, by welding, flanging or bolting ofend fittings.

At that time, the laying operation illustrated in FIG. 1a can beresumed. Supply ship 19 can either accompany laying ship 1, inparticular if it has a sufficient capacity to contain the section offlexible tubular conduit 3 necessary for the next transfer, or leaveagain toward the port for supplies. The use of a plurality of supplyships 19 to perform the transfer of flexible tubular conduits 3 duringeach transfer stage illustrated in FIG. 1b does not go outside the scopeof this invention.

In FIG. 2, it is possible to see an example of laying flexible tubularconduits using a second process according to this invention. In theexample illustrated in FIG. 2, laying ship 1 directly lays a flexibletubular conduit 3 provided by a supply ship 19. In the exampleillustrated in FIG. 2, supply ship 19 comprises a cage 20 similar tocage 2 of laying ship 1.

Tubular conduit 3 directly forms a small chain between guide means 4 ofship 1 and guide means 4' of ship 19. As illustrated by arrows 15, thesetwo ships advance side by side having approximately the same speed.Their distance is, for example, approximately equal to 40 meters.

Advantageously, as soon as supply ship 19 has used up its supply offlexible tubular conduits, it is replaced by a new full supply ship (notrepresented in the figure).

It is possible to fill cage 2 of laying ship 1 as well as to leave itempty. Filled cage 2 makes it possible to continue laying flexibletubular conduits 3 in the absence of supply ship 19. An empty cage 2makes ship 1 lighter, and more stable.

In FIG. 2, it is possible to see the mechanism for loading and unloadingflexible tubular conduits in cage 2. For the loading, a coiler arm 21 isused whose displacement symbolized by arrow 23 makes possible thewinding of flexible tubular conduit 3 approximately in a spiral. Also, acoiler arm 22 following the same movement illustrated by arrow 23 makesit possible to unload flexible tubular conduit 3 from cage 2 to, forexample, guide means 4.

Of course, the use of a laying ship 1 not comprising means for storingflexible tubular conduits does not go outside the scope of thisinvention.

In FIG. 3, it is possible to see the third example of the processaccording to this invention. In this case, two sections of tubularconduits 3 and 3' are transferred simultaneously between the supply shipand the laying ship. Flexible tubular conduit 3 provided by supply ship19 is directly laid by laying ship 1. Simultaneously, a tubular conduit3' is provided by a supply ship 19' from its storage means 20'. Conduit3' is stored in cage 2 of ship 1. If laying ship 1 is in the process oflaying flexible tubular conduit 3, three ships 1, 19, 19' advancesimultaneously with approximately the same speed as illustrated by arrow15.

The two small chains of flexible tubular conduits 3 and 3' can beprovided by the same supply ship or, as illustrated in FIG. 3, bydifferent supply ships. The fact of loading cage 2 of ship 1 gives it alaying autonomy corresponding, for example, to 30,000 m of flexibletubular conduits of an inner diameter approximately equal to 7.5 cm(three inches in using the English measurement) corresponding to alaying time of 6 to 7 days, or 5000 meters of flexible tubular conduitsand an inner diameter approximately equal to 30 cm (twelve inches inusing the English measurement) corresponding to a laying time of one dayto one and a half days. This example is given for flexible tubularconduits 3 intended to be laid at a depth of 1000 meters andwithstanding an internal working pressure of 210 bars (approximately3000 p.s.i., in using the English measurements). The autonomy providedby the presence of cage 2 makes it possible to free supply ship 19and/or 19'.

The laying ship and the supply ship have approximately the same averagespeed. This speed is, for example, equal to the laying speed, forexample, between several meters per hour to 800 meters per hour. Thisspeed is preferably between 300 and 500 meters per hour, typically 300meters per hour. The transfer of flexible tubular conduit between thestorage means of ship 19 and the laying ship can, for example, beperformed at the linear speed of 500 meters per hour.

In FIG. 4, it is possible to see a fourth process example according tothis invention using a laying ship 1 comprising two storage cagesreferenced 2 and 2'. In FIG. 4a, cage 2 makes possible the laying offlexible tubular conduits 3 on the ocean floor, as symbolized by arrow14, cage 2' being loaded with a tubular conduit 3' from cage 20 of asupply ship 19. Once cage 2' of supply ship 1 is loaded with flexibletubular conduit 3', supply ship 19 is freed. This can occur before theend of the laying of flexible tubular conduit 3 from cage 2. Supply ship19 can then be supplied in a port for, as illustrated in FIG. 4b, makingpossible the supply of the cage from which flexible tubular conduit 3 isin the process of being laid. Of course, the use of a plurality ofsupply ships 19 taking over from each other with laying ship 1 does notgo outside the scope of this invention.

In the example illustrated in FIG. 4a, laying ship 1 performs the layingfrom cage 2 placed immediately after derrick 5. Cage 2' loaded withflexible tubular conduit 3' from ship 19 is located at the back of theship. Of course, the use of cages 2, 2' distributed on both sides ofopening 8 of ship 1 does not go outside the scope of this invention.

In the example illustrated in FIG. 4b, flexible tubular conduit 3 islaid on the floor from the back cage, which, in FIG. 4b, carriesreference 2. Tubular conduit 3 is brought by horizontal guide means upto guide means 4 making possible its passage to the vertical at thelevel of derrick 5. The cage closet to opening 8 being used fortransferring tubular conduit 3' from a supply ship 19, in FIG. 4b,carries reference 2'. The exchange of roles of cages 2, 2' makes itpossible to assure the continuity of the laying of flexible tubularconduits on the ocean floor.

It is evident that during the transfer, the laying ship and the supplyship have approximately the same average speed. During the laying, thesupply ship controls the speed at the average speed of the laying ship.

The invention applies mainly to the laying of flexible tubular conduitsof great length intended for the transport of hydrocarbons as well asthe laying of deep-sea electric cables on the ocean floor.

We claim:
 1. A process for transferring flexible conduits from at leastone supply ship to a laying ship for laying said conduits onto an oceanfloor, comprising transferring a flexible conduit to be laid on saidocean floor by continuous unrolling at a laying site from at least onesupply ship to a laying ship, said supply ship and said laying shipbeing separated from one another and connected only by said flexibleconduit, wherein said flexible conduit is gradually transferred fromsaid supply ship to a storage means located on said laying ship.
 2. Aprocess for transferring flexible conduits from at least one supply shipto a laying ship for laying said conduits onto an ocean floor, inaccordance with claim 1, wherein a conduit portion located between saidat least one supply ship and said laying ship has the shape of acatenary.
 3. A process for transferring flexible conduits from at leastone supply ship to a laying ship for laying said conduits onto an oceanfloor, in accordance with claim 1, wherein a conduit portion locatedbetween said at least one supply and said laying ship floats on thesurface of the water.
 4. A process for transferring two sections offlexible conduits from at least one supply ship simultaneously to alaying ship for laying said two sections of conduits onto an oceanfloor, comprising transferring said two sections of flexible conduits bycontinuous unrolling at a laying site from at least one supply ship tosaid laying ship, wherein one section of flexible conduits is loadedinto a storage means located on said laying ship for future laying andsaid other section of flexible conduit is transferred to said layingship for direct laying onto said ocean floor.
 5. A process fortransferring two sections of flexible conduits from at least one supplyship simultaneously to a laying ship for laying said two sections ofconduits onto an ocean floor, in accordance with claim 4, wherein aportion of each of said two sections of flexible conduit located betweensaid laying ship and at least one supply ship has the shape of acatenary.
 6. A process for transferring two sections of flexibleconduits from at least one supply ship simultaneously to a laying shipfor laying said two sections of conduits onto an ocean floor, inaccordance with claim 4, wherein a portion of each of said two sectionsof flexible conduit located between said laying ship and at least onesupply ship floats on the surface of the water.
 7. A process fortransferring flexible conduits from at least one supply ship to a layingship for laying conduits onto an ocean floor comprising transferring aflexible conduit to be laid on said ocean floor by continuous unrollingat a laying site from at least one supply ship to a storage cage locatedon said laying ship, wherein said laying ship comprises at least twostorage cages and transfers flexible conduit to said ocean floordirectly from a first storage cage while a second storage cage is beingfilled by a supply ship; once said first storage cage is emptied, saidlaying ship then lays flexible conduit located in said second storagecage onto said ocean floor, while said first storage cage is beingrefilled by said supply ship.
 8. A process in accordance with claim 7,wherein a portion of said flexible pipe located between said supply shipand said laying ship has the shape of a catenary.
 9. A process isaccordance with claim 7, wherein a portion of said flexible pipe locatedbetween said supply ship and said laying ship floats on the surface ofthe water.